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Global Positioning System/Transcript
Transcript Text reads: The Mysteries of Life with Tim & Moby A signal pings. A boy, Tim, and a robot, Moby, climb a mountain path. TIM: Man, are we ever lost. Tim and Moby check their map. TIM: Okay, are we on this mountain, or that one? MOBY: Beep. Tim reads from a typed letter. TIM: Dear Tim and Moby, How can a GPS tell you where you are? From, Simon. TIM: That's a really good, strangely appropriate question. GPS stands for Global Positioning System. With a GPS receiver, you can pinpoint your location on Earth at any time, in any place. Images shows Moby reading his handheld GPS device in four different locations. TIM: Around thirty GPS satellites orbit 20,200 kilometers above the Earth. Each sends out a signal that someone with a GPS receiver can use to determine their latitude, longitude, and altitude at any time. MOBY: Beep beep. An animation shows GPS satellites orbiting Earth. TIM: Oh, latitude and longitude are coordinates on a map. A map shows latitude as the horizontal lines, and longitude as the vertical lines on a grid overlaying the map. TIM: Altitude is how high up you are, like if you're in an airplane or on a mountain. An animation shows an airplane flying over lower and higher elevation surfaces shown on a grid. TIM: At any given time and place, at least four satellites are always above the horizon. An animation shows satellites sending signals in the sky over a mountainous landscape. TIM: Each GPS satellite transmits a special code via radio waves. An animation shows the code above a satellite. TIM: The GPS receiver knows what the code should look like at any given time so it can use this code to figure out how far away the satellite is. An animation shows the receiver reading code from a satellite's signal. It depicts a map of the area on a screen. MOBY: Beep. TIM: Well, remember that radio waves travel at the speed of light. The speed of light is really fast, about 300,000 kilometers per second, but it's not instant. The signal from the satellite will lag behind the matching code in the receiver by just a little bit. The receiver automatically measures this lag and uses it to calculate the distance from the satellite. An animation illustrates how the satellite's signal lags behind the receiver's signal. MOBY: Beep. TIM: Ah, but remember, we're measuring the distance from four satellites. The first satellite tells you you're somewhere on the edge of this sphere. The sphere intersects the Earth at this circle, so if you're on the ground, you know you're somewhere on that circle. The second satellite narrows down your location to two points on the ground, where the circles intersect. The third satellite pinpoints one location on the ground. The fourth satellite helps correct for differences in the clock onboard the satellites and in your receiver, and nails down your position pretty much exactly. Animations show the point at which all three circles intersect, to illustrate how satellites pinpoint location. MOBY: Beep. Beep. Beep. TIM: Many receivers combine this information with built-in maps to help people figure out where they are in the world. An animation shows a receiver with a built-in grid map. A blinking circle on the map indicates its location. TIM: I just wish we had one. I don't know how we're going to find our way back to the road. MOBY: Beep. Moby points his finger in one direction. TIM: How do you know we're supposed to go that way? MOBY: Beep. TIM: I don't know; it seems like every time I trust you we end up in more trouble than when we started. But I guess that way's as good as any. Tim looks and walks in the direction Moby pointed while Moby checks a GPS receiver. Moby hides the receiver behind his back from Tim's view. TIM: Hey, you coming? MOBY: Beep.Category:BrainPOP Transcripts